The present invention relates to an apparatus useful for fluorinating organic compounds, or more particularly to a reactor suitable for the fluorination of organic compounds on a commercial scale. The reactor may also be used for other chemical processing that require heating or cooling. The reactor finds particular use in the manufacture of hydroflurocarbons (HFCs). The reactor of the invention includes a large volume reactor vessel lined with a loose fluoropolymer liner that is highly resistive to corrosion.
It is known in the art that hydrofluorocarbons (HFCs) are popular substitutes for chlorofluorocarbons (CFCs) and hydrochlorofluorocarbons (HCFCs) for use as refrigerants, heat transfer agents, blowing agents and propellants because HFCs do not deplete the ozone layer of the atmosphere. HFCs are typically prepared by fluorinating a chlorinated organic compound with a fluorination agent such as hydrogen fluoride in the presence of a fluorination catalyst. This reaction may be conducted in either the liquid or gas phase. Generally, the liquid phase fluorination process is preferred because the reaction is controlled at relatively lower temperatures which results in less by-product formation due to decomposition.
Liquid phase fluorination, however, uses and generates corrosive compounds, such as hydrogen fluoride, hydrogen chloride, and Lewis acid catalysts, which form superacids. These superacids tend to corrode the reactor vessel in which the reaction is conducted, even reactors comprised of corrosion-resistant materials such as Inconel 600, NAR25-50MII, Hastelloy C, Hastelloy G-30, duplex stainless steel, and Hastelloy C-22. Corrosion of the reactor compromises the structural integrity of the reactor and reduces its useful life. Therefore, a need exists to minimize reactor corrosion.
One method of reducing such corrosion is taught in Japanese Kokai Patent Application Publication No. 233102(1995). In this publication, a method is disclosed for the liquid phase fluorination of a chlorinated organic compound in a reactor made or lined with a fluorine containing resin. The method involves gaseous feeds of hydrogen fluoride and chlorinated organic compound. Because the process is restricted to gaseous feed streams, it is limited in the type of HFCs it can produce. Chlorinated organic compounds having two or more carbon atoms tend to decompose before reaching their gaseous state. Thus, as a practical matter, the process disclosed in this publication can only be used to produce fluorinated methanes.
The aforementioned Japanese publication also states that when heat transfer through the reactor is necessary, which is usually the case in liquid phase fluorination, the fluorine containing resin liner should be applied using a molding method. The only molding method identified therein is rotary-baked molding.
Generally, reactors having a molded liner, such as a rotary-baked or sprayed-on liner, are not suitable for large-scale commercial production. Reactors having such liners must be baked in large kilns or ovens, which are expensive and frequently unavailable. Indeed, fitting a large reactor, for example, greater than about a 1,000 gallons, with a baked liner is impractical.
A molded liner not only imposes practical limitations on the reactor, but also introduces structural limitations. It has been found that molded liners tend to be permeable and, under high pressures and over time, reactants tend to penetrate the liner and develop pressure between the liner and the reactor wall. Therefore, while a rotary-baked, fluorine-resin liner may minimize reactor corrosion, its structural limitations nevertheless limit the reactor's useful lifetime.
To overcome these problems which are inherent with rotary-baked or spray molded liners, it is now popular in the art to use a loose liner to line the inside of reactors. As the term implies, a loose lining is one which is fabricated from a sheet of protective material in a desired configuration and which is then installed into the intended equipment. Capped flanges on the ends of the vessel are typically used to pressure fix the ends of the lining to the ends of the vessel.
Regarding fluorination reactions in particular, reactors that are lined with a loose lining fabricated from fluoropolymer materials have been found to be useful for combating the corrosive conditions present in certain small-scale liquid phase fluorination reactions. For example, U.S. Pat. No. 5,902,912 teaches using a 50 gallon (appx. 6.7 ft3) loosely lined reactor vessel for producing less than one million lbs/yr of fluorocarbons in pilot scale operations. However, it has been determined that conventional non-corroding, fluoropolymer-lined reactors suffer from a variety of problems when utilized in large-volume processes, e.g. at least about 1000 gallons (appx. 134 ft3). Such problems include body flange seal leaking, liner flexing stress and shrinking, as well as leakage of hydrogen fluoride through the liner. Therefore, a need exists for non-corrosive reactors that can be used for the commercial scale production of fluorinated compounds. More particularly, there is a need for a high integrity, fluoropolymer lined metallic vessel having a heat input/output capability suitable to manufacture HFCs, such as HFC-143a, HFC-32, HFC-245fa, HFC-227ea, HFC-236fa, HFC-365mfc, etc., and to conduct other highly corrosive applications on a commercial scale.
The present invention provides a non-corroding and highly reliable apparatus useful for liquid phase hydrofluorination of organic compounds. Furthermore, the invention provides a reactor apparatus that avoids the problem of liner flexing and shrinking during disassembly of the reactor, and thus extending the operational life of the liner.